Water or steam injection can be used for power augmentation and/or the control of nitrous oxide emissions in a combustion turbine powered electrical generating plant. The cost of the water used in this process can be significant, and it is becoming increasingly difficult in some areas to obtain a permit to use water for power generation. Accordingly, it is desirable to recover water from the exhaust stream of a combustion turbine.
Water is a natural byproduct of the combustion of hydrocarbon fuels. It is known that cooling the exhaust stream from a combustion turbine in a condenser to below the precipitation temperature of the moisture in the exhaust gas will result in the condensation of a portion of the moisture contained in the exhaust gas. The quantity and percentage of the moisture recovered is a function of the temperature to which the exhaust can be cooled by the condenser. Ambient air is commonly the ultimate heat sink for such condensers, and the ambient air temperature thus determines the amount of moisture that can be removed by the condenser. In an arid desert environment, where it is most likely that water recovery will be desired, the daytime ambient air temperature may be over 100° F. or even 110° F. and the effectiveness of water removal by an air-cooled condenser is limited.
It is known that sulfur contained in the fossil fuel burned in a combustion turbine will result in the presence of sulfuric acid in the combustion turbine exhaust stream. While the concentration of sulfur may be relatively low, the sulfur compounds, particularly sulfuric acid, will condense from the exhaust gas stream at a slightly higher temperature than the temperature at which water will condense, and thus a locally high concentration of sulfuric acid may develop on portions of the tubes of the condenser. Sulfuric acid is very corrosive to the carbon steels that are normally used to manufacture condenser tubes, and thus stainless steel, having a higher cost, must be used.
U.S. Pat. No. 5,843,214 describes a system for capturing a condensable vapor such as water in a combustion turbine exhaust stream. This system uses a fog of water particles to cause moisture in the combustion turbine exhaust to condense to form a warm rain of condensate. The patent illustrates the condensate being cooled using seawater as the ultimate heat sink. Seawater may be sufficiently cold to provide an adequate level of moisture removal from the combustion turbine exhaust; however, such a system would be far less efficient in a high temperature desert environment where only air-cooled condensate is available.